The present invention relates generally to electronic circuits, and, more particularly, to a bridgeless power factor correction converter.
A power factor of an electrical circuit is determined using a ratio of real power to apparent power, where the real power is associated with a load of the electrical circuit, and the apparent power is the power supplied to the electrical circuit. The power factor is indicative of the efficiency of the circuit. An efficient circuit will have a power factor in the range of 0.8-1, where 1 is ideal.
Today's power supplies often include a power factor correction (PFC) converter in order to improve the efficiency of the power supply. One example of a PFC circuit is a critical conduction mode (CRM) totem-pole bridgeless PFC circuit. This circuit includes a zero-current detection (ZCD) circuit and a bridgeless PFC converter. The bridgeless PFC converter includes transistors in a totem-pole arrangement and an inductor. A power factor close to unity is achieved by carefully controlling the switching of the transistors. The transistors are switched based on a detection of a zero-current state across the inductor by the ZCD circuit.
The ZCD circuit uses auxiliary windings to detect the zero-current state based on a voltage induced in the auxiliary windings. However, the induced voltage is bipolar, so a rectification circuit is needed to detect the induced bipolar voltage. A sampling circuit also is required to sample voltages used for detecting the zero-current state. The sampling circuit and the rectification circuit increase the area required by the ZCD circuit and thus by the bridgeless PFC system.
Other implementations of the ZCD circuit include current transformer (CT) sensors that detect the zero-current state. However, using multiple CT sensors increases area as well as power consumption. In addition, other bridgeless PFC systems may include additional hardware circuitry or use software-based methods for controlling the bridgeless PFC converter. However, accuracy issues are prevalent. Thus, there is still is room for improvement in CRM bridgeless PFC systems.